Preload dependency of left atrial pump function in hypertrophic cardiomyopathy.

In our previous study, we reported that the left atrial contribution to left ventricular filling was decreased to a greater extent in patients with hypertrophic cardiomyopathy than in those with myocardial infarction or normal subjects during lower body negative pressure (LBNP)-induced preload reduction. To clarify the factors responsible for this difference in response, we examined changes in left atrial hemodynamic and M-mode echocardiographic indices during LBNP in patients with hypertrophic cardiomyopathy and myocardial infarction. The same degree of decrease in left atrial preload and afterload was found in both groups. Moreover, we detected no change in the left atrial fractional shortening during left atrial systole (%LAFS) in patients with hypertrophic cardiomyopathy, in contrast to a significant increase found in patients with myocardial infarction. These results showed that the greater decrease in the left atrial contribution in hypertrophic cardiomyopathy during LBNP could not result from differences in changes in left atrial preload or afterload, suggesting that it may be closely related to limitations in the compensatory augmentation of left atrial contractility.